Network Working Group P. Marques
Request for Comments: 4684 R. Bonica
Updates: 4364 Juniper Networks
Category: Standards Track L. Fang
L. Martini
R. Raszuk
K. Patel
J. Guichard
Cisco Systems, Inc.
November 2006
Constrained Route Distribution for
Border Gateway Protocol/MultiProtocol Label Switching (BGP/MPLS)
Internet Protocol (IP) Virtual Private Networks (VPNs)
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The IETF Trust (2006).
Abstract
This document defines Multi-Protocol BGP (MP-BGP) procedures that
allow BGP speakers to exchange Route Target reachability information.
This information can be used to build a route distribution graph in
order to limit the propagation of Virtual Private Network (VPN)
Network Layer Reachability Information (NLRI) between different
autonomous systems or distinct clusters of the same autonomous
system. This document updates RFC 4364.
Marques, et al. Standards Track [Page 1]RFC 4684 Route Target (RT) Constrain November 2006Table of Contents
1. Introduction ....................................................2
1.1. Terminology ................................................3
2. Specification of Requirements ...................................4
3. NLRI Distribution ...............................................4
3.1. Inter-AS VPN Route Distribution ............................4
3.2. Intra-AS VPN Route Distribution ............................6
4. Route Target Membership NLRI Advertisements .....................8
5. Capability Advertisement ........................................9
6. Operation .......................................................9
7. Deployment Considerations ......................................10
8. Security Considerations ........................................11
9. Acknowledgements ...............................................11
10. References ....................................................11
10.1. Normative References .....................................11
10.2. Informative References ...................................12
1. Introduction
In BGP/MPLS IP VPNs, PE routers use Route Target (RT) extended
communities to control the distribution of routes into VRFs. Within
a given iBGP mesh, PE routers need only hold routes marked with Route
Targets pertaining to VRFs that have local CE attachments.
It is common, however, for an autonomous system to use route
reflection [2] in order to simplify the process of bringing up a new
PE router in the network and to limit the size of the iBGP peering
mesh.
In such a scenario, as well as when VPNs may have members in more
than one autonomous system, the number of routes carried by the
inter-cluster or inter-as distribution routers is an important
consideration.
In order to limit the VPN routing information that is maintained at a
given route reflector, RFC 4364 [3] suggests, in Section 4.3.3, the
use of "Cooperative Route Filtering" [7] between route reflectors.
This document extends the RFC 4364 [3] Outbound Route Filtering (ORF)
work to include support for multiple autonomous systems and
asymmetric VPN topologies such as hub-and-spoke.
Although it would be possible to extend the encoding currently
defined for the extended-community ORF in order to achieve this
purpose, BGP itself already has all the necessary machinery for
dissemination of arbitrary information in a loop-free fashion, both
within a single autonomous system, as well as across multiple
autonomous systems.
Marques, et al. Standards Track [Page 2]RFC 4684 Route Target (RT) Constrain November 2006
This document builds on the model described in RFC 4364 [3] and on